1. Field of the Invention
This invention is related to lasers, and more particularly, to horizontal emitting, vertical emitting, beam shaped, distributed feedback (DFB) lasers by growth over a patterned substrate.
2. Description of the Related Art
A laser diode is a semiconductor device that emits light in a stimulated manner when electrically biased in the forward direction. The feedback required to reach auto-oscillation is provided by mirrors, usually obtained by cleaved facets, or by mirror-coated facets for horizontal in-plane lasers, or by dielectric multi-layer mirrors for vertical surface emitting lasers (VCSELs). Some lasers incorporate a dispersive element, such as a grating, providing distributed feedback (DFB) to achieve single mode emission.
Lasers generally comprise a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a pn junction. When biased forwardly, electrons are injected into the junction from the n-region and holes are injected from the p-region, usually in a thin emitting layer called a quantum well (QW). The electrons and holes in the quantum well release energy in the form of photons as they recombine. The wavelength of the light, and therefore its color, depends on the bandgap energy of the materials forming the pn junction.
As semiconductor materials have improved, the efficiency of semiconductor devices has also improved and new wavelength ranges have been used. Gallium nitride (GaN) based lasers are probably the most promising in a variety of applications. GaN provides efficient illumination in the ultraviolet (UV) to amber spectrum when alloyed with varying concentrates of indium (In), for example.
Unfortunately, besides huge materials challenges, nitride lasers are difficult to manufacture. Cleaved facets have a low reflectivity, due to the low refractive index of nitrides. In addition, cleavage is hard to achieve because a sapphire substrate is typically used with nitride lasers.
To obtain good nitride lasers, it is necessary to obtain good mirrors using a planar fabrication technique. Other desirable properties include vertical emission, high power, single mode emission, etc. However, these properties, especially vertical emission, are extremely hard to obtain, as the high quality mirrors required for vertical cavity surface-emitting lasers (VCSELs) prove extremely difficult to manufacture.
The present invention aims at solving these challenges by using device growth techniques over a patterned substrate, wherein the pattern provides the function of a mirror, optical confinement layer, grating, wavelength selective element, beam shaping element or beam directing element.